mirror of https://github.com/qTox/qTox
docs(apparmor): Add README about AppArmor
Document AppArmor profile usage, troubleshooting and other concerns.reviewable/pr5577/r2
Vincas Dargis
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# Hardening qTox with AppArmor
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qTox can be confined with AppArmor on Linux to reduce attack vectors in case remote code execution exploit is being used. Please note that [MAC's](https://en.wikipedia.org/wiki/Mandatory_access_control) (of course) does not guarantee perfect security, but it will:
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- Deny access to your `~/.bashrc`, `~/.ssh/*` `~/.config/path/to/your/password/manager/file`, etc.
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- Deny creating autostart entries (in `~/.config/autostart`, etc).
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- Deny launching random executables (like `sudo`, `su`, etc...).
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- And more.
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Consider using additional security measures like [Firejail](https://firejail.wordpress.com/) to improve security even more.
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Please also note that not all distributions has full AppArmor feature set available. For example, Debian (at least up to Debian 10 (buster)) does not have network, DBus mediation available. Also, X Server, shared user configuration files (like `~/.config/QtProject.conf`, caches, etc), opening web links via unconfined browsers introduces additional attack vectors, too. So please be cautious even with number of security measures applied.
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**AppArmor profile attaches only to `/usr/bin/qtox` and `/usr/local/bin/qtox` executables by default**. See [Tuning permissions](#tuning-permissions) for custom setups.
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## Installing profile
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Select AppArmor profile from appropriate `security/apparmor/X` subdirectory depending on what AppArmor version is available for your Linux distribution release:
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- 2.13.2
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- Debian 10 (buster) (or newer)
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- openSUSE Tumbleweed
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- 2.12.1
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- Debian 9 (stretch) or older
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- Ubuntu 19.04 or older
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To enable AppArmor profile on your system, run prepared install script:
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```
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cd security/apparmor/x.y.z
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sudo ./install.sh
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```
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Restart `qTox` if it was already running before enabling AppArmor profile.
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## Checking if qTox is actually confined
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Run `aa-status` command line utility and check if `qTox` is listed within `X processes are in enforced mode.` list:
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```
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sudo aa-status
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...
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21 processes are in enforce mode.
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/usr/lib/ipsec/charon (2421)
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/usr/sbin/cups-browsed (839)
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...
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/usr/bin/qtox (16315) qtox
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...
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```
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Alternatively, use `ps` and `grep`:
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```
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ps auxZ | fgrep qtox
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qtox (enforce) vincas 16315 2.0 1.1 1502292 180220 ? SLl 12:21 0:38 /usr/bin/qtox
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```
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If OK it's marked as `(enforce)`. `uncofined` means AppArmor profile is not attached to the process, no confinement is being applied.
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## Troubleshooting
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If you believe that some feature is unavailable, or some files you need access to are inaccessible due to enforced AppArmor profile, check system logs for the hints.
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On Debian/Ubuntu:
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```
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sudo fgrep DENIED /var/log/syslog
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```
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On openSUSE, OR if you have `auditd` daemon installed:
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```
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sudo fgrep DENIED /var/log/audit/audit.log
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```
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You will see messages like this:
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```
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type=AVC msg=audit(1549793273.269:149): apparmor="DENIED" operation="open" profile="qtox" name="/home/vincas/.config/klanguageove
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rridesrc" pid=3037 comm="qtox" requested_mask="r" denied_mask="r" fsuid=1000 ouid=1000
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```
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This means that `r`ead access was denied to the file `/home/vincas/.config/klanguageoverridesrc`, owned by you (ouid 1000), by AppArmor profile `qtox` (available in `/etc/apparmor.d/usr.bin.qtox`).
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Please create issue if you detect new AppArmor `DENIED` messages and you believe that these denials are relevant for other users too. Meanwhile, workaround by adding manual rule. DO NOT modify `/etc/apparmor.d/usr.bin.qtox` directly! See [Tuning permissions](#tuning-permissions) for fixing access issues.
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## Tuning permissions
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If you need access to files (for file sharing) other than from your `$HOME` or mounted media, create/modify `/etc/apparmor.d/tunables/usr.bin.qtox.d/local` file and append writable path variable:
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```
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@{qtox_additional_rw_dirs} += /path/to/some/directory
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```
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Alternatively, if you need more custom/advanced rules (not only for file access), create/modify `/etc/apparmor.d/local/usr.bin.qtox` file.
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Rule example for reading only, recursively (note the comma!):
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```
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/path/to/directory/** r,
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```
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For reading and writing, recursively:
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```
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/path/to/directory/** rw,
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```
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Restart AppArmor to reload profiles after modifications:
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```
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sudo systemctl restart apparmor
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```
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If AppArmor restart fails, check syntax errors by invoking AppArmor parser directly:
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```
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sudo apparmor_parser -r /etc/apparmor.d/usr.bin.qtox
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```
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For custom installations, when `qTox` executable is not `/usr/bin/qtox` or `/usr/local/bin/qtox`:
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1. create `/etc/apparmor.d/tunables/usr.bin.qtox.d/local`, adding `@{qtox_prefix} += /path/to/your/custom/install/prefix` line.
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2. modify `/etc/apparmor.d/usr.bin.qtox` profile attachement path: `profile qtox /usr{,local}/bin/qtox,/path/to/your/qtox_executable {`
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Restart AppArmor and [check](#checking-if-qtox-is-actually-confined) if `qTox` process under custom path is actually confined.
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## Other resources
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Check [Debian](https://wiki.debian.org/AppArmor), [Ubuntu](https://wiki.ubuntu.com/AppArmor), [Upstream AppArmor](https://gitlab.com/apparmor/apparmor/wikis/home) Wiki pages for more info.
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